This invention relates to an optical disk, such as a video disk, a compact disk, or a compact disk read-only memory, and an optical disk device for recording information on an optical disk and for reproducing the information therefrom.
An optical disk has a recording surface on which information is recorded as surface irregularities or surface deformations representative of the information. Typically, the surface irregularities consist of pits formed along a record track with a land left between two adjacent ones of the pits. The pits and the lands have different lengths along the record track in accordance with the information. In connection with the different lengths, it is possible to understand that the surface irregularities are formed along the record track with a predetermined desity of record.
The optical disk has a very large memory capacity because each of such record tracks is only about one micron wide. In addition, it is possible to manufacture a great number of replicas or reproductions from a waster or prototype optical disk. The optical disks are therefore believed to be prosperous as media for use as electronic publications.
It should, however, be noted that a conventional optical disk is for use only in reproducing or reading the information which is already recorded thereon as basic information. It is impossible for a reader of the basic information to voluntarily add additional information, such as an underscore or a comment, to the basic information in contrast to conventional printed publications. It is also impossible for an author of the basic information to partly change the basic information for a revised edition. This incapability of recording and reproducing additional information is disadvantageous to a wider use of the optical disks as electronic publications.